Meteorite Impacts and Mass Extinctions

The impact of a space object with a size greatest than about 1 km would be expected to be felt over the entire surface of the Earth. Smaller objects would certainly destroy the ecosystem in the vicinity of the impact. similar to the effects of a volcanic eruption, but larger impacts could have a worldwide effect on life on the Earth. We will here first consider the possible effects of an impact, and then discuss how impacts may have resulted in mass extinction of species on the Earth in the past. Regional and Global Effects: Again, we 8S humans have no firsthand knowledge of what the effects of an impact of a large meteorite or comet would be. Still, calculations can be made and scaled experiments can be conducted to estimate the effects. The general consensus is summarized here.

Massive earthquake up to Richter Magnitude 13, and numerous large magnitude, aftershocks would result from the impact of a large object with the Earth.

The large quantities of dust put into the atmosphere would block incoming solar radiation. The dust could take months to settle back to the surface. Meanwhile the Earth would be in a state of continual darkness and temperatures would drop throughout the world, generating global winter like conditions. A similar effect has been postulated for the aftermath of a nuclear war (termed a nuclear winter). Blockage of solar radiation would also diminish the ability of photosynthetic organisms, like plants, to photosynthesize. Since photosynthetic organisms are the: base of the food chain, this would seriol1sly disrupt all ecosystems.

Widespread wildfires ignited by radiation from the fireball as the object passed through the atmosphere would be generated. Smoke from these fires would further block solar radiation to enhance the cooling effect and further disrupt photosynthesis.

If the impact occurred in the oceans, a large steam cloud would be produced by the sudden evaporation of the seawater. This water vapor and CO2 would remain in the atmosphere long after the dust settles. Both of these gases are greenhouse gases which scatter solar radiation and create ~ warming effect. Thus, after the initial global cooling, the atmosphere would undergo global warming for many years after the impact.

lf the impact occurred in the oceans giant tsunamis would be generated. For a 10 km diameter object., the leading edge would hit the seafloor of the deep ocean basins before the top of the object had reached sea level. The tsunami from such an impact is estimated to produce waves from 1 to S km high. These could easily flood the interior of continents.

Large amounts of nitrogen oxides would result from combining Nitrogen and Oxygen in the atmosphere due to the shock produced by the impact. These nitrogen oxides would combine with water in the atmosphere to produce nitric acid which would fall back to the surface as acid rain, resulting in the acidification of surface waters.

The Geologic Record of Mass Extinction: It has long been known that extinction of large percentages families or species of organisms have occurred at specific times in the history of our planet. Among the mechanisms that have been suggested to have caused these mass extinctions, have been large volcanic eruptions, changes in climatic conditions, changes in sea level, and, more recently, meteorite impacts. While the meteorite impact theory of mass extinctions has become accepted by many scientists for particular extinction events, there is still considerable controversy among scientists. An impact with a large object could have caused at least some of the mass extinction events, as it would certainly seem possible given the effects that an impact could have. Human Hazards: It should be clear that even if an impact of a large space object did not cause the extinction of humans, the effects would cause a natural disaster of proportions never witnessed by the human race. Here we first look at the chances that such an impact could occur, then look at how we can predictor provide warning of such an event, had finally discuss ways that we might be able to protect ourselves from such an event. Risk - It is estimated that in any given year the odds that you will die from an impact of an asteroid or comet are about 1 in 20,000. Prediction a n d Warning - It is estimated that over 90% of NEOs have not yet been discovered. Because of this with our present knowledge there is a good chance that the only warning we would have is the flash of light from the fireball as one of these objects entered the Earths atmosphere. Scientists have proposed the "Spaceguard Survey" to find and track all of the large NEOs. If such a survey is carried out, we could predict the paths of all NEOs and have years to decades to prepare for an NEO that could impact the Earth. Mitigation -Impacts are the only natural hazard that we can prevent from happening by either deflecting the incoming object or destroying it. Of course, we must first know about such objects and their paths in order to give us sufficient warning to prepare a defense.